This invention relates to the preparation of protein hydrolyzates, and particularly non-gelling protein hydrolyzates, from tannery limed splits.
In the preparation of non-gelling protein hydrolyzates or protein hydrolyzates of zero bloom strength from collagenous material, it is known to heat the collagenous material in a cook tank in the presence of sulfite ions to minimize the development of color. Such processes are disclosed, for example, in U.S. Pat. No. 3,308,113, granted Mar. 7, 1967; U.S. Pat. No. 3,683,939, granted Aug. 15, 1972 and U.S. Pat. No. 3,738,913, granted June 12, 1973, all in the names of Vernon L. Johnsen, Eugene V. Matern and Raymond S. Burnett.
The collagenous material which may be used in such processes includes materials from such sources as bones, skins, hides, sinews, fatty tissues and the like.
The sulfite ion source is generally calcium bisulfite, separately prepared by passing liquid sulfur dioxide into a slurry of calcium carbonate until the solution becomes clear. Sulfur dioxide is disclosed as a possibly advantageous source of sulfite ions in that its addition does not introduce ash forming constituents (e.g. at col. 2, lines 56 to 72 of U.S. Pat. No. 3,308,113), but its use is restricted to "jacketed pressure vessels that are not heated by direct steam." For vented vessels, the patentees disclose sulfite salts "because of their greater stability under the conditions of the pressure cooking," and because the "use of sulfur dioxide gas is uneconomical [in such vessels] due to loss in the continuously vented gases." In addition, the continuous venting of sulfur dioxide could constitute a health and safety hazard.
In the processing of hides for leather preparation, the hides, removed from slaughtered animals, are first soaked in brine, then dried for preservation before being shipped to a tannery.
The tanner first washes out the salt from the hides and then tumbles the hides in a lime (calcium hydroxide) bath containing sodium sulfide to totally remove hair from the hides. During this process, the hides absorb about 2% to 3% by weight of lime (calculated as calcium oxide).
The hides are then split in thickness to an outer thickness which makes the best leather, and an inner thickness which makes a poorer leather. The hides are split in such a way as to obtain a maximum area of the more desirable outer thickness; and the inner thickness is therefore frequently uneven, particularly at its edges. The edges are usually trimmed away before the split hides are tanned because tanning chemicals are expensive and there is no desire to waste them on trimmings which are not suitable for leather. The trimmings from hides after lime treatment, and particularly the trimmings from the inner thickness of the hides, are called "limed splits" at the tannery; and it is this material which is used as a collagen source in this invention.
Tannery limed splits have been used as a source of collagen in the preparation of gelatin and glue; and more recently have been used in the preparation of protein hydrolyzates of zero bloom strength in a vented cook tank utilizing live steam as a heat source. In the latter case, sulfite ions were charged to the cook tank in the form of a preformed calcium bisulfite solution; and there was no conception that molecular sulfur dioxide could be charged to a vented cook tank with substantially no losses where the collagenous material was limed splits.